I bring a few big zip lock bags in my bag. They come in handy often. I use one to seperate wet things from the rest of my luggage and another to seperate dirty clothes. A mesh bag will allow your clean clothes to get stinky and/or wet.
A zip lock bag is also my washing machine for socks, underwear and the occasional T-shirt. Put dirty clothes, very little detergent and some warm, hot or cold water (depending on what you're washing). Shake well, drain, add rinse water, shake, drain, repeat rinsing until no more soap suds are draining out. Then wring your clothes (I use a car chamois because it absorbs a lot of water and wrings nearly dry) and hang them overnight to dry (provided you packed the right kind of clothes).
I still like to use a self service laundry about once per trip to give everything a good wash but this works well for a small daily load.